High-performance on-chip spectrometers and spectrum analyzers

Abstract

We disclose an on-chip photonic spectroscopy system capable of dramatically improving the signal-to-noise ratio (SNR), dynamic range, and reconstruction quality of Fourier transform spectrometers. Secondly, we disclose a system of components that makes up a complete on-chip RF spectrum analyzer with low-cost and high-performance.

The invention claimed is: 
     
       1. A method of operating a spectrometer, the method comprising:
 splitting incident light into a first portion and a second portion; 
 transmitting the first portion through at least one delay stage switchable between a first waveguide having a first optical path length and a second waveguide have a second optical path length different than the first optical path length; 
 transmitting the second portion through a reference waveguide; 
 attenuating at least one of the first portion or the second portion to compensate for loss imbalance between the at least one delay stage and the reference waveguide; 
 detecting interference between the first portion with the second portion; and 
 determining a spectrum of the incident light based on the interference of the first portion and the second portion, 
 wherein attenuating the first portion comprises modulating a relative phase between the first portion and the second portion such that the interference of the first portion with the second portion has a null at a desired frequency. 
 
     
     
       2. The method of  claim 1 , wherein transmitting the first portion through the at least one delay stage comprises transmitting the first portion through a plurality of cascaded delay stages. 
     
     
       3. The method of  claim 1 , wherein transmitting the first portion through the at least one delay stage comprises transmitting a first fraction of the first portion through the first waveguide and a second fraction of the first portion through the second waveguide. 
     
     
       4. The method of  claim 1 , wherein transmitting the first portion through the at least one delay stage comprises transmitting the first portion through the first waveguide and further comprising:
 switching the at least one delay stage from the first waveguide to the second waveguide; and 
 transmitting the first portion along the second waveguide. 
 
     
     
       5. The method of  claim 1 , wherein attenuating the first portion increases an extinction ratio of the interference between the first portion and the second portion. 
     
     
       6. The method of  claim 1 , further comprising, before detecting the interference:
 coupling a fraction of the first portion out of the at least one delay stage; 
 detecting an intensity of the fraction of the first portion; and 
 adjusting a setting of the at least one delay stage based on the intensity. 
 
     
     
       7. A spectrometer comprising:
 a beam splitter to split incident light into a first portion and a second portion; 
 a delay stage, in optical communication with a first output of the beam splitter and switchable between a first waveguide having a first optical path length and a second waveguide have a second optical path length different than the first optical path length, to delay the first portion with respect to the second portion; 
 a reference waveguide, in optical communication with a second output of the beam splitter, to guide the second portion; 
 an attenuator, in optical communication with at least one of the delay stage and the reference waveguide, to attenuate at least one of the first portion or the second portion; 
 a detector, in optical communication, via the attenuator, with the delay stage and the reference waveguide, to detect interference of the first portion with the second portion; 
 a processor, operably coupled to the detector, to determine a spectrum of the incident light based on the interference of the first portion and the second portion; 
 a tap, in optical communication with the delay stage, to couple a fraction of the first portion out of the delay stage; and 
 a monitor photodetector, in optical communication with the tap, to monitor an intensity of the fraction of the first portion. 
 
     
     
       8. The spectrometer of  claim 7 , wherein the delay stage is a first delay stage and further comprising:
 a second delay stage, concatenated with the first delay stage and switchable between a third waveguide having a third optical path length and a fourth waveguide having a fourth optical path length different than the third optical path length, to further delay the first portion with respect to the second portion. 
 
     
     
       9. The spectrometer of  claim 7 , wherein the delay stage is configured to guide a first fraction of the first portion through the first waveguide and, simultaneously, to guide a second fraction of the first portion through the second waveguide. 
     
     
       10. The spectrometer of  claim 7 , wherein the delay stage is configured to be switched between a first state in which the first portion propagates through the first waveguide and a second state in which the first portion propagates through the second waveguide. 
     
     
       11. The spectrometer of  claim 7 , wherein the attenuator is configured to increase an extinction ratio of the interference between the first portion and the second portion. 
     
     
       12. The spectrometer of  claim 7 , wherein the attenuator is configured to adjust a relative phase between the first portion and the second portion. 
     
     
       13. The spectrometer of  claim 7 , further comprising:
 a phase modulator, in optical communication with the beam splitter, to modulate a relative phase between the first portion and the second portion such that interference of the first portion with the second portion creates a null at a desired frequency. 
 
     
     
       14. A spectrometer comprising:
 a beam splitter to split incident light into a first portion and a second portion; 
 a delay stage, in optical communication with a first output of the beam splitter and switchable between a first waveguide having a first optical path length and a second waveguide have a second optical path length different than the first optical path length, to delay the first portion with respect to the second portion; 
 a reference waveguide, in optical communication with a second output of the beam splitter, to guide the second portion; 
 an attenuator, in optical communication with at least one of the delay stage and the reference waveguide, to attenuate at least one of the first portion or the second portion; 
 a detector, in optical communication, via the attenuator, with the delay stage and the reference waveguide, to detect interference of the first portion with the second portion; 
 a processor, operably coupled to the detector, to determine a spectrum of the incident light based on the interference of the first portion and the second portion; and 
 a phase modulator, in optical communication with the beam splitter, to modulate a relative phase between the first portion and the second portion such that interference of the first portion with the second portion creates a null at a desired frequency. 
 
     
     
       15. The spectrometer of  claim 14 , wherein the delay stage is a first delay stage and further comprising:
 a second delay stage, concatenated with the first delay stage and switchable between a third waveguide having a third optical path length and a fourth waveguide having a fourth optical path length different than the third optical path length, to further delay the first portion with respect to the second portion. 
 
     
     
       16. The spectrometer of  claim 14 , wherein the delay stage is configured to guide a first fraction of the first portion through the first waveguide and, simultaneously, to guide a second fraction of the first portion through the second waveguide. 
     
     
       17. The spectrometer of  claim 14 , wherein the delay stage is configured to be switched between a first state in which the first portion propagates through the first waveguide and a second state in which the first portion propagates through the second waveguide. 
     
     
       18. The spectrometer of  claim 14 , wherein the attenuator is configured to increase an extinction ratio of the interference between the first portion and the second portion.